A variety of multi-channel optical communications modules exist for simultaneously transmitting and/or receiving multiple optical data signals over multiple respective optical channels. A Multi-channel optical transmitter module, as that term is used herein, denotes an optical communications module having multiple optical transmit channels for simultaneously transmitting multiple optical signals over one or more optical waveguides (e.g., optical fibers). A Multi-channel optical receiver module, as that term is used herein, denotes an optical communications module having multiple optical receive channels for simultaneously receiving multiple respective optical signals over one or more optical waveguides. A Multi-channel optical transceiver module, as that term is used herein, denotes an optical communications module having multiple optical transmit channels and multiple optical receive channels for simultaneously transmitting and receiving multiple optical signals over one or more optical waveguides.
For each of these different types of parallel optical communications modules, a variety of designs and configurations exist. A typical electrical subassembly (ESA) layout for a multi-channel optical transceiver module includes a circuit board, such as a printed circuit board (PCB), and various electrical components mounted on the circuit board, such as one or more controller chips, a laser driver chip, a transimpedance amplifier (TIA) chip, and a receiver chip. A typical optical subassembly (OSA) for a multi-channel transceiver module includes multiple optoelectronic components (i.e., laser diodes and photodiodes), which are mounted on the circuit board and electrically coupled to the ESA via bond wires and/or via electrical traces of the PCB. An optical coupling system of the module couples optical signals generated by the laser diodes into ends of one or more optical waveguides (e.g., optical fibers) and couples optical signals passing out of ends of one or more optical fibers onto the photodiodes.
The newest generation of high-speed multi-channel optical transceiver modules for long reach applications use externally-modulated lasers (EMLs) as the light sources rather than directly-modulated (DM) lasers. While different types of EMLs exist, the type of EMLs that are typically used for long reach applications comprise an electro-absorption modulator (EAM) integrated with a distributed feedback (DFB) laser in the same integrated circuit to form an integrated EAM-DFB laser. In general, EAM-DFB lasers are preferred over DM lasers for long reach applications because EAM-DFB lasers have lower chirp and can be operated at higher bandwidths than DM lasers.
However, use of an EAM-DFB lasers in a multi-channel optical transceiver module requires a complex scheme for controlling the EAM bias voltage and the DFB bias current and for monitoring the EAM photocurrent. An ESA implementation for carrying out such a complex scheme in, for example, a four-channel optical transceiver module, sometimes referred to as a Quad-channel optical transceiver module, would require multiple controller IC chips and other electronic components that would be expensive to design and manufacture. Such a complex scheme would also consume a large amount of area on the PCB of the ESA, have low manufacturing yield and would be difficult to thermally manage.
Accordingly, a need exists for a control device that is capable of controlling the EAM bias voltage and DFB bias current, that is capable of monitoring the EAM photocurrent, that can be manufactured at relatively low cost with relatively high yield, and that can be implemented in a relatively small area.